1. Field of Invention
This invention relates generally to syringe devices adapted to collect blood samples. More particularly, the invention relates to syringes capable of collecting blood samples that are purged of any gaseous contaminants.
2. Description of the Prior Art
Syringe devices conventionally include tubular bodies receiving pistons or sealing members connected to plungers. The syringe devices have been adapted to discharge trapped air from an interior chamber, defined by the position of the sealing member, into which chamber a medicament or blood sample is drawn. The structures, and even the specific purposes for removing the air, vary widely.
The time-honored technique for removing air from the interior chamber of a syringe is simply inverting the syringe and squeezing out a portion of the aqueous contents of the interior chamber, presumably with any trapped air. This method is somewhat effective in the preparation of medicaments for injection into a patient, but the indiscriminate discharge of blood in a hospital environment is unsanitary.
There are many prior art syringe devices that utilize some type of vent between the interior chamber and the atmosphere. What differs among the various syringe devices is the manner in which the vent, once formed, is closed at the proper time. An example of a blood-gas syringe device is seen in U.S. Pat. No. 4,206,768 to Bailey, that patent having common ownership with the present application. In the Bailey patent, a vent is formed by a string or thread passed across the sealing member. The string is adapted to be manually wound onto a plunger, sealing the vent, after the blood sample is obtained and the gas has been purged across the sealing member via the vent. The plunger is rotatably connected to the sealing member.
Hollow plungers are one type of structure used for venting air from the interior chamber to ambient pressure. Such a device is seen in U.S. Pat. No. 1,643,531 to Wolf, wherein a sample of medicament is drawn, air is purged along the hollow plunger, the vent through the plunger is capped, and the syringe is utilized to inject the contents of the syringe. This specific device is not adapted for use in blood-gas analysis because capping the plunger does not seal off air within the plunger from the sample. Wolf also requires capping the plunger for effective use, as opposed to self-sealing of the vent at the interior chamber. An extra manual step is required in virtually all of the syringe devices to seal a vent once made.
Filter elements are commonly utilized in syringe devices, primarily for purposes of preventing particulate matter from entering the medicament or the patient. To Applicant's knowledge, however, filters have not been utilized to seal the vent, within a certain range of pressures, of a blood-gas syringe, though hydrophobic filters, which allow gas to pass until they are wetted, as by blood, are commercially available. Hydrophobic plastic is suggested as a material for an integral plunger-sealing member in U.S. Pat. No. 3,656,480, to Rubricius, but the hydrophobic properties are not necessary for the purposes of the invention.
Use of fabric filter elements to inhibit the flow of blood are known. U.S. Pat. Nos. 3,960,139 and 3,978,846 to Bailey disclose filters that partially, and preferably totally, restrict the flow of blood after gases have been allowed to flow therethrough.
The prior art does not show a syringe device for obtaining a gas-free blood sample that automatically seals off the blood sample obtained once predetermined conditions are reached. The conditions relate to volume of the blood sample and purging of air associated with the blood sample.
A copending application having Ser. No. 359,292, filed Mar. 18, 1982, entitled "Syringe With Means For Allowing Passage Of Air While Preventing Passage Of Blood To Obtain Gas-Free Blood Sample", which is a continuation of Ser. No. 279,453, filed July 1, 1981, entitled "Syringe With Hydrophobic Filter", now abandoned does show automatic sealing off of the blood sample within the syringe by use of a hydrophobic filter. Though the apparatus disclosed in that application is fairly effective, as long as breakthrough pressure is not exceeded, in utilizing a hydrophobic filter to stop the flow of blood across the filter once the filter is wetted by the blood, the filter will not stop the passage of air across the filter. Thus, unless the blood sample is obtained in such a manner that the interior chamber of the syringe is totally filled with blood, air can flow back across the hydrophobic filter into the interior chamber and come into contact with the blood sample. Even when no bubbles of air are initially present, as a result of the syringe being packed in ice for transport to an area where testing is to be performed, the blood cools and therefore contacts, permitting air to cross the filter.
Because of its simplicity, many hospitals and doctors still utilize the expulsion method with medicaments, but a need has existed for a simple, effective yet inexpensive, syringe device for obtaining a blood sample free of air contamination.